Overview of VPCs and vSwitches - VPCs and vSwitchs| Alibaba Cloud Documentation Center

VPCs and vSwitches

A VPC is a private network deployed on Alibaba Cloud.

Note You cannot directly deploy cloud resources in a VPC. You must deploy cloud resources in vSwitches of a VPC.

A vSwitch is a basic network device in a VPC and is used to connect cloud resources. You can deploy a VPC only in one region and cannot deploy a VPC across regions. However, a VPC covers all zones of the region to which the VPC belongs. You can create one or more vSwitches in a zone to create one or more subnets for the VPC. VPCs and vSwitches

CIDR blocks and IP addresses

VPCs support both IPv4 and IPv6. By default, VPCs use IPv4. You can enable IPv6 based on your business requirements. For more information, see Enable IPv6 for a VPC and Enable an IPv6 CIDR block for a VPC network.

VPCs support the dual-stack mode. In dual-stack mode, resources in a VPC can communicate through both IPv4 and IPv6 addresses. IPv4 and IPv6 addresses are independent of each other. Therefore, you must configure routes and security groups for both IPv4 and IPv6 addresses.

The following table lists the differences between IPv4 and IPv6 addresses.


Item	IPv4 VPC	IPv6 VPC
IP address format	An IPv4 address is 32 bits in length and contains four groups. Each group consists of at most three decimal digits.	An IPv6 address is 128 bits in length and contains eight groups. Each group consists of four hexadecimal digits.
Feature status	By default, IPv4 is enabled for all VPCs.	You can manually enable IPv6.
VPC CIDR block size	The subnet mask of a VPC CIDR block can range from `/8` to `/28`.	The subnet mask of a VPC CIDR block is `/56`.
vSwitch CIDR block size	The subnet mask of a vSwitch CIDR block can range from `/16` to `/29`.	The subnet mask of a vSwitch CIDR block is `/64`.
Whether you can specify a CIDR block	You can specify an IPv4 CIDR block.	You cannot specify an IPv6 CIDR block. The system automatically assigns an IPv6 CIDR block to your VPC from the IPv6 address pool.
Supported instance families	Supported by all instance families.	Not supported by specific instance families. For more information, see Instance families.
Whether ClassicLink connections are supported	ClassicLink connections are supported.	ClassicLink connections are not supported.
Whether elastic IP addresses (EIPs) are supported	IPv4 EIPs are supported.	IPv6 EIPs are not supported.
Whether gateways are supported	VPN gateways and NAT gateways are supported.	VPN gateways and NAT gateways are not supported.

By default, IPv4 and IPv6 addresses provided for VPCs support only communication over private networks. Cloud resources deployed in different vSwitches that belong to the same VPC can communicate with each other over private networks.

If you want to connect a VPC to another VPC, you can create VPC peering connections or use Cloud Enterprise Network (CEN) or VPN gateways.
If you want to connect a VPC to a data center, you can purchase VPN gateways, Express Connect circuits, or Smart Access Gateway (SAG) devices.

For more information, see Network connection overview.

To enable cloud resources in a VPC to communicate with the Internet, configure the following items:

Through IPv4 addresses
You can configure NAT gateways or associate EIPs with Elastic Compute Service (ECS) instances in a VPC. This way, the ECS instances can communicate with the Internet through IPv4 addresses.

For more information, see Associate an EIP with an ECS instance and Use the SNAT feature of an Internet NAT gateway to access the Internet.
Through IPv6 addresses
To enable cloud resources in a VPC to communicate with the Internet through IPv6 addresses, you must purchase an IPv6 Internet bandwidth plan. You can configure egress-only rules for IPv6 addresses. This allows cloud resources in the VPC to access the Internet through IPv6 addresses. However IPv6 clients cannot access the cloud resources over the Internet.

For more information, see Enable and manage IPv6 Internet bandwidth and Create and manage an egress-only rule.

Routes

The system automatically creates a system route table and adds system route entries to control the traffic of the VPC. A VPC has only one system route table. You cannot create or delete a system route table. System route tables

You can create and associate custom route tables with vSwitches to facilitate network management. A vSwitch can be associated with only one route table. For more information, see Create and manage a route table.

If multiple route entries match the destination IP address, the route entry with the longest subnet mask prevails and is used to determine the next hop. This ensures that the traffic is routed to the most precise destination. You can also add a custom route entry to route traffic to a specified destination. For more information, see Add and delete routes.